1. Field of the Invention
The invention relates to a holder for fuel elements in a nuclear reactor, in particular in a boiling water reactor, with a core shroud and with a forged core grid positioned above the core shroud, in which the core shroud and core grid are connected to one another through the use of an adapter ring. The invention also relates to a method for repairing a holder for fuel elements, in particular in a boiling water reactor, in which a core grid is removed from the upper end of a core shroud and a new forged core grid is connected to the core shroud via an adapter ring.
The internal fittings of a reactor, in particular of a boiling water reactor, include a holder for fuel elements. An integral part of this holder is a core grid, through the orifices of which the fuel elements run. This ensures that the fuel elements can be positioned in a desired way. Another part of the holder is the core shroud which laterally surrounds the reactor core formed from the fuel elements.
When such a holder is being repaired, it may be necessary to exchange the core grid. For this purpose, the latter is separated from the upper end of the core shroud and replaced by a new core grid. This new core grid may be a forged core grid which is more stable than a core grid assembled from metal sheets. The height of such a forged core grid is less than the height of other core grids. It is therefore necessary to connect the new forged core grid to the core shroud via an adapter ring, so that the holder has the same height as heretofore.
It has heretofore been customary to weld the adapter ring to the new core grid. Large-volume weld seams were necessary for this purpose, although these are susceptible to damage. Furthermore, due to the welding operation, heat is transferred into the material of the core grid and of the adapter ring, but the effect of such heat is to increase the susceptibility of the material to corrosion, in particular to stress cracking corrosion. Moreover, the core grid and core shroud are particularly at risk in the region of the weld seams, since radioactive radiation is additionally conducive to corrosion.